The invention relates to a control arrangement for actuating a shut-off valve and method of operation.
To keep bodies of water clean it is necessary for waste water to be passed into sewage plants. However, this is often not possible because of disproportionally high costs for conventional sewer systems or because of difficult local conditions, such as lacking natural gradients, low population density, disadvantageous subsoil or transition through an area of a protected water table. But even for such problem cases there is a possibility for providing disposal by means of a sewage plant, if an underpressure drainage system or a "vacuum drainage" is employed.
An appropriate vacuum drainage comprises as essential components connecting pits in houses with a currentless-operating control arrangement and shut-off or drain-off valves, a connecting line system with systematically disposed high and low points and a vacuum station with waste water storage tanks, waste water pumps, vacuum pumps, technical measuring and control devices.
For conveying the waste water, it first flows out of the buildings via conventional gravity-action building connecting lines to a shaft, for example located at the property boundary, in which the shut-off valves, which are controlled exclusively pneumatically, and the associated control arrangement are housed.
When a set static pressure has been reached, the shut-off valve is opened by the mechanism contained in the control arrangement and the waste water is drained off through the vacuum line. After a few seconds the valve is closed as a function of time by means of a spring force and vacuum.
The waste water itself collects at the low points in the line system and is pushed gradually over subsequent high points in the direction of the vacuum station by spurts of air. Then the water is transported via a pressure and gravity-action line from the collecting tank of the vacuum station to the sewage plant by conventional waste water pumps.
In this case the control device associated with the shut-off valve should allow an automatic adaptation to the amounts of waste water to be drained off and the operating conditions of the waste water system.
A control arrangement of the type described at the outset is known under the designation "AIRVAC". Time control takes place via a pressure-adjustable chamber which at the start is charged with atmospheric pressure. There is no clear OPEN/CLOSED position of the second valve directing the underpressure to the shut-off valve. This means that the amounts of the waste water or the waste water-air mixture per opening cycle of the shut-off valve are not clearly defined. This can lead to malfunctions, in particular in case of large amounts of waste water. It is furthermore disadvantageous that the drain-off time depends, in a manner which is unfavorable for the entire system, on the available underpressure, since the opening times themselves depend on the prevailing underpressure.
It is furthermore disadvantageous that opening of the second valve, which releases the underpressure to the shut-off valve, can already take place at low underpressure which, however, is not sufficient for drain-off. This leads to the danger that waste water is lifted into the area of the line exposed to freezing and can freeze out there.
A pneumatic control device for a shut-off valve of an underpressure waste water line is known from DE 37 27 661 A1. At least one control valve and a minimum underpressure valve, besides a first valve operated by a static pressure and a structurally elaborate time control device, are required to assure exact setting and dependable operation of the control device.
An elaborate construction and assembly is required because of the complex mechanical construction of the time control device in particular which, among other things, comprises a diaphragm piston with a hollow pin which is guided in a guide bushing for opening or closing the control valves.
DE 38 23 515 A1 describes an aspirating pistol by means of which it is possible to drain off waste water from a reservoir by means of underpressure. In addition to an drain-off valve which closes and opens an underpressure line through which the waste water is drained off, a control valve is required which can be manually or automatically operated. So that the control valve can be closed when the underpressure is reduced, because of which the shut-off valve is disconnected from the underpressure, the control valve has a valve piston on which, as a function of the position of the valve piston, axially and/or radially spring-loaded balls act which are required for closing the control valve.